1. Field of the Invention
The present invention relates to an image forming apparatus and a density unevenness correction method in the image forming apparatus.
2. Description of Related Art
Lately, since density unevenness occur on an output image, an image forming apparatus such as a multi-functional peripheral, printer etc., includes a density adjustment function. It is known that such density unevenness occur from change in output density due to mechanical factors such as change of condition of the image forming apparatus over time, mounting position of the optical writing device such as a laser unit, etc., optical path length, distortion of lens, charging condition of drum, condition of intermediate transfer section or the like, or change in surrounding environment.
As an image forming apparatus including the density adjustment function, for example, according to Japanese Patent Application Laid-Open Publication No. 2005-246646 there is provided an image forming apparatus which stores image data with a color pattern where a color patch of a predetermined color and a color patch of colors in which a predetermined value is shifted with respect to each color component from a predetermined color are positioned so that the change of color phase is substantially continuous, and the image forming apparatus also stores identification information corresponding with the color patch. Then, the image forming apparatus outputs the color pattern based on the image data of the color pattern and performs color correction of the image data using the color correction table according to the input identification information.
However, it is known that density unevenness changes according to image forming conditions such as number of screen lines of the image formed, paper type and basis weight of the paper on which the image is formed, speed of lines which change due to the above factors, etc. Especially, there are various paper types and basis weight of paper, and various combinations are used by the user. Therefore, it is difficult to previously set the correction value according to the various image forming conditions, and there is a problem that density unevenness due to image forming conditions cannot be corrected.